Colasterion: A Reply to a Nameles Answer against The Doctrine and Discipline of Divorce was published on or near March 4, 1645 in response to the anonymous tract, An Answer to the Doctrine and Discipline of Divorce. "Colasterion" is a Greek word that literally translates as "the place of punishment," and, as such, the reader should regard Colasterion as Milton's verbal thrashing of the anonymous answerer. He also takes opportunities here to upbraid several other men, co-champions with him in the cause against prelacy and in support of puritan reform of the Church of England. Milton had reason to believe that William Prynne, Herbert Palmer and Joseph Caryl were part of a "Champarty," or cabal, of erstwhile comrades in Parliament that directed the writing and production of the anonymous An Answer; Joseph Caryl's name as licenser appears in the tract along with a paragraph implicitly denouncing Milton's ideas on divorce as the work of an "unstaid minde." These men feared that Milton was taking reform too far in a radical and populist direction.

Colasterion and Tetrachordon appeared almost simultaneously. In Tetrachordon, Milton makes his case for changing canon law by marshalling detailed interpretations of the four chief places in the Bible that teach about marriage. In Colasterion, Milton answers the anonymous objections to his teaching on marriage and divorce point for point but always in the context of ridiculing the answerer as a fraudulent scholar, an embarrassingly poor lawyer, and a lower-class serving man with a mind in the gutter. Not only, alleges Milton, does he argue in bad faith and with faulty logic, but because he is not a gentleman, he simply cannot comprehend what Milton might mean by "fit conversation" in marriage; he always will think of it as carnal relations and nothing more.

The copytext for the Milton Reading Room edition of Colasterion is based on the reproduction of a copy in the British Library supplied online by Early English Books Online at (Wing (2nd ed.) / M2099 Thomason / E.271[11]).